Electronic amplifier circuits



Patented Aug. 5, 19,52

ELECTRONIC AMPLIFIER CIRCUITS Thomas J. Boland, Wakeeld, Mass., assgnorto Raytheon Manufacturing Company, a corporation of Delaware ApplicationNovember 5, 194s, serial No. 58,460v

11 Claims. (Cl. 343-75) This invention relates in general to tunedelectronic amplifier circuits having variable band width, and moreparticularly to methods and means for varying theband width of suchcircuits.

It is an object of the invention to provide improved means forcontrolling and varying the band Width of a tuned electronic amplier.

It is another obiectto devise such means which willalso provide controlof the gain of the amplifier.

It is an additional'object of the invention to devise band width controlmeans which are particularly suitable for use in echo distancedetersystems, such as underwater sounding and ranging systems. forexample.

It is afurther object ,of the invention to devise such control meanswhich can he operated from the now available A. V. C. voltage sources inradio receivers and the like.

Other and further objects of the invention will Abecome apparent fromthe description of certain embodiments thereof which follows, referencebeing had to the accompanying drawings, wherein: v

Fig. 1 is an electrical schematic of the invention as it may be employedin an underwater echo distance determining system;

Fig. 2 is a simplified electrical schematic of another embodiment of theinvention; and

Fig. 3 illustrates the invention as it may be employed in a radioreceiver.

Referring now'to Fig. 1, a transducer I0 is shown in the form of A ablock, representative of anyof the lmown forms of underwater soundtransducers. A source of unidirectional power whichrmay be a battery II, a resistor I2, a capacitor I3, and the transducer I0 are connectedtogether in a series circuit, whereby the capacitor I3 may be charged tothev battery potential' through the transducer I0. A normally openswitch I 4, operated momentarily to a closed position by a rotatable camI 5provides a momentary short circuit `around the battery II andresistor I2.` The capacitor I3 discharges via this short circuit throughthe transducer I0, thereby shockexciting the transducer into oscillationat its natural frequency. A second capacitor I6 is connected in shuntwith the battery II, and provides a bypass around the battery for thetransducer oscillations when the switch I4 is opened.

I'he rst tube 20 of the receiver amplifier of the system is coupled viaits control grid 22 to the junction point 2| of .the resistor I2 andcapacitor I 3 througha current-limiting resistor 2 Y 23 and a couplingcapacitor 24- in series. A grid coupling resistor 25 is connected at oneside to the 'junction of the current-limiting resistor 23 and thecoupling capacitor 24, and at the other sidetoground. g. Thedetails ofconstruction and operation of the circuit arrangements just describedare set forth and claimed in copending application, Serial No. 27,210,led May '15, 1948, of Fryklund, now Patent No. 2,561,851, dated July 24,1951. The operation, briefly, is as follows.l When the switch I4 isclosed, point 2l is connected to ground,

thereby short-circuiting the input totube 20 at the same time that thetransducer vIl! Vis excited. This arrangement provides protection forthe receiver and the indicator that is used therewith during theproduction of a transmitted pulse.

It has been found, however, that the sudden change of potential on thegrid 22 with respect to the cathode 26 of the rst tube 20 causes theproduction of sharp transintscin the tuned circuits of the ampliiier,and, particularly when the amplier is sharply tuned, these tunedcircuits become shock-excited, or ring in the same 2-`manner as thetransducer I0. The present in- :,terminal offthe batteryy .21 isgrounded. and a vention has as one of its features the elimination ofsuch ringing and a consequent increase in the useful range of thesounding or ranging system.

The circuit of the rst tube 20 includes a tuned circuit 30, comprisingan inductor 3| and a capacitor 32 connected in parallel between theanode 33v and the positive terminal of a battery 2l via acommon'B-lterminal 34. The negative bypass capacitor 28 is connected inshunt with the battery. The cathode 26. of the tube is connected toground via a biasing resistor 35 and a shunt connected bypass capacitor36. The suppressor Liii-,grid 3l 'is directly connected to the cathode,

5,5; arrangement beinggknown-'asstagger tumn l g..

while theV screen grid 38 is connected to the cathode via abypasscapacitor. 39. The screen grid derives its potential from the B+terminal 34 through a dropping resistor 40.' The tube 20 preferably asharp cut-oil pentode, for example a type 6AU6. The output ofthe rsttube20vis coupled to a second similar amplifying stage 42 through a couplingcapacitor 43 and a. coupling resistor `MI. As jwill be appreciated bythose .'skilledin th'e art, Aa particular 'receiver may involve anydesired number of tuned amplifying stages, and these stages may besharply tuned to the same frequency or .v sharply tuned each to aslightly diierentfrequency, the-latter A pairof reversely-connectedtriodes 5I and 52 are connected in shunt with the tuned circuit 30through a capacitor 53. Considering the tuned circuit 30 as the sourceof the alternating signal which is being amplified, the shunt patharound it consists of the capacitor 53, the parallel-connected triodes5l and 52., and the battery bypass condenser 28 in series, the circuitof the shunt path being completed through suitable ground connections asshown. The capacitors 53 and 28 are of suiciently large size withrespect to the frequency of the signals being handled-so that theirreactance is low at the operating frequency, and the shunt path isessentially a resistance. The magnitude of the resistance is controlledby the potential which is furnished to the grids 55 and 5B of triodes 5land 52, respectively, with respect to their respective cathodes 57 and58. The anode 6I of the rst triode 5I is directly connected to thecathode 58 of the second triode 52, and these two elements are thenconnected through a relatively large resistor 62, having a valueV of amegohm or more, to ground'. The anode 63 of the second triode 52 andthecathode 51 of the rst triode 5I are also both connected to ground. Apermanent cut-oil' bias is furnished to the grids 55l and 56 by a biasbattery 65, which has its positive terminal grounded. and its negativeterminal connected to both grids in parallel through a dischargeresistor 6E A charging capacitor 6l is connected fn shunt with thebattery 65v and theres'istor 66 in series; 'A diode 10 has its cathode'Il connected to the junction point I2 of the resistor 66, capacitor 51,and the grids 55 and 56, and itsanode 13 connected to a terminal 14 atwhich positive pulses T5 synchronized with transmitted pulses are m'ade.available in a manner that will presently be described. 'I'he positivepulse passes .through the diode 'I0 and places a charge on the chargingcapacitor 61 which overcomes the bias of the bias battery 65 and rendersthe triodes 5I and 52 conductive each during one of the half-cycles Vofthe signal wave. The charge on the charging capacitor 61 leaks oithrough the discharge resistor 66 so that the triodes 5I and 52' are,within a fixed time interval, again rendered non-conductive. The largeresistor 62 provides a direct current return around the triodes 5I and52.

The pulse is derived. from thev battery Il which provides the energyfrom which the transducer pulse is derived. A voltage selection tap TIis connected to one terminal 'I8 of a normally open switch 19. The other`terminal 8| of this switch is connected .to' the pulse terminal 14. .Arotatable cam 82 momentarily closes the switch I9 at the sarne time thatthe Virst-'mentioned cam I5 momentarily closes the transducer keyingswitch I4. For this purpose, the twocams I5 and 82 can be arranged onthe same operating shaft 83. When the pulse switch 'I9 is closed, acircuit is completed from the tap 'I7 through the switch I9 andYterminal 'M- ,to the anode 'I3 of the diode 10, then from 'the cathodeH through the charging capacitor 61 to ground, and via ground to thenegativetermina'l of the transducer battery I I. This 'connection issuch that the diode 'I0 becomes conductive and the burst of current thatflows therethrough when the switch 'I5 is momentarily closed constitutesthe short pulse l5. Y

The operation of the invention is as follows. Whenv the transducer Iisoperated to produce a pulse of transmitted energy, the control pulse I5charges the charging capacitor 61, thereby 4 rendering the triodes 5Iand 52 conductive. The impedance of the shunt path across the tunedcircuit 30 is lowered. The effect of this is to increase the band widthof the tuned circuit and simultaneously to lower the gain of the amplierstage in which it is included. From another point ofview it-may besaidthat the tuned amplier stage is in fact detuned. o r renderedaperiodic. As such, the amplier stage is not now easily shock-excited,either by transients due to the energization of the transducer or bytransients due to spurious signals and disturbances originating at closeranges. -It is common experience that spuriousv transients originatingby nearby sources seriously disturb tuned amplifiers. Depending upon thetime constant of the parallel circuit of the charging capacitor 6l andthe dischargeresistor 66, the conductivity of the triodes 5I and 52 willeventually: fall to zero, and these tubes again become non-conductive.At this time the shunt path around the tuned circuit has such a highresistance .that it constitutesv pracf tically an open circuit. 'Underthis condition,

the sharp tuning of the amplifier stage is restored, and signals of theoperating frequency' equipment, for example, thegain and suscepti- Vbility to disturbance are reduced automatically when shoal soundings arebeing taken and increased automatically ,for deep soundings.

A further advantage v of the invention is that l when the band widthisincreased, the response time of the amplifierjcorrespondinglyincreases.

Thus, in a depth sounding system the presentv invention makes possibleShoal sounding in very shallow water by providing fast response of thekindavailable with aperiodic ampliers, while also providing theadvantages of a tuned amplier having higher gain and higher sensitivityfor deep sounding.

The connection o f -the tube triodes 5I and 52 in Fig. l is such thatthese tubesare operative on both halves ofthe cyclev of the alternatingcurrent wave. Fig. 2 illustrates another embodiment, wherein thelblocking capacitor 53 and the direct current return-resistor 62 'areeliminated, and the variable shunt across the tuned circuit 3B is purelyresistive. In this other embodiment, two ltriodes 9! and 92 areconnected in parallel and in the same 'direction across the tuned cir'-cuit 3B. The reiiirn of the circuit through the capacitance' 28 ofthebattery 2T is not illustrated as it is the same as in Fig. 1. Thepositive pulse 'I5 is again furnished toV the' charging capacitor 51from a; battery 93 under the control of a normally open 'momentarily'operated switch `94 through the diode 10. The battery 93 and switch 94are the equivalent'of the section of the transducer battery II that istapped by the tap-I7 in Fig. 1 and the'c'a'incperated switch 19. The

signal isbrought to the grid 22 of the flrsttubeA 20 by way of an inputterminal 95 and .taken from the fflrst stage to the succeedingstage`'by; way'cf an'output terminal 96 following the signalk couplingcapacitor 43. In all other respects,I the circuit of Fig. 2 is the sameas the circuitof Fig. l. Two triodes 9| and 52 'are shown, since it willbe convenient to ,employ a double triade. tube, namely, .atube whereinthe elements'ofi both triodes are contained in the same envelope, and

to arrange the external connections in the `manner desired.

The embodiment of the invention illustrated in Fig. 2 operates in thesame manner as that illustrated in Fig. l with the additionalimprovement that a purely resistive shunt is `provided across the tunedcircuit 30. On the other hand, the arrangement of the triodes 9| and 92is such that the shunt is provided only during those half-cycles of thesignal wave when the anodes are positive with respect to the cathodes.Both embodiments are operative, however, to produce the desired results.

Referring now to Fig. 3, which illustrates the invention as it may beemployed in a radio receiver, the shunt circuit around the tuned circuit30 is controlled by the voltage furnished from the A. V, C. system 99,commonly found in the receiver. The voltage from the A. V. C. system isapplied directly across the resistor 66 in the biasing circuit of theshunt tubes, of which only one cathode 57 and one control grid 55 areillustrated in Fig. 3. The bias battery 65 may be retained if desired.

The invention is conveniently employed in connection with theintermediate frequency amplifier of the receiver and controls the bandwidth of this amplifier, and hence of the receiver. The A. V. C. voltageconnection is such that on strong local signals the band width isincreased, permitting response to a wider band of audio-frequencies. Toaccomplish this, the A. V. C. voltage should be applied to increase theconductivity of the shunt circuit on strong local signals. Then, fordistant or weaker stations, the resistance of the shunt circuit isincreased, and the selectivity and sensitivity of the receiver areincreased therewith.

Many other variations and equivalents of the invention will occur tothose skilled in the art, and it is accordingly intended that the claimsthat follow shall not be limited by the details of the embodiments thatare shown and described herein, but only by the prior art.

What is claimed is:

l. In combination, in an echo distance measuring system having searchpulse producing means and echo pulse receiving means operative at aprescribed frequency, an electronic amplifier in circuit with saidreceiving means, said amplifier including a parallel-resonance circuittuned substantially to said prescribed frequency across which ampliiiedreceived signals are developed, circuit means connected in shunt withsaid parallel-resonance circuit, means coupled with said search pulseproducing means for reducing the resistance of said shunt-connectedmeans each time a search pulse, is produced, and means operativethereafter for gradually increasing said resistance at a controlledrate.

2. In combination, in an echo distance measuring system having Searchpulse producing means and echo pulse receiving means operative at aprescribed frequency, an electronic amplier in circuit with saidreceiving means, said amplifier including a parallel-resonance circuittuned substantially to said prescribed frequency across which amplifiedreceived signals are developed, electron tube means having ananode-cathode path connected in shunt with said parallelresonancecircuit, means coupled in operation with said search pulse producingmeans for increasing the conductivity of said electron tube means eachtime a search pulse is produced, and

6i? means operative thereafter for gradually decreasing saidconductivity. at acontrolled rate;

3. In combination, in an echodistance measuring system having searchpulse producing .means and echo pulse receiving means operative at aprescribed frequency.. an` electronic. amplifier in circuit with saidYreceiving means, said amplifier including. a parallel-.resonancecircuittuned substantially to said prescribed frequency across whichampliiied receivedisignalsare developed, electron tube means .having ananode-cathode path connected. in shunt .with said parallelresonancecircuit, .means normally Aproviding a cut-oir bias potential to saidelectron tube means, means coupled with said search pulse Producingmeans rendering said electron tube means conductive each time a. searchpulse is produced, and means operative thereafter for graduallydecreasing the conductivity of .said electron tube means to the cut-offpoint at a controlled rate.

4. In combination, in an echo distance measuring system havingv searchpulseA producing means and echo-pulse .receiving means operative at aprescribed frequency, .an electronic amplifier in circuit withsaidreceiving'means, ,said amplier including a parallel-resonance. circuittuned substantially Ato said prescribed frequency across whichamplied-,receivedfsignals are; developed. electron tube means having.'anv anode-cathode path connected Vintil.;said parallelresonancecircuit, meansynormally :providing a cut-off bias potential toVsad=electrqn tube means, means coupled Withaid .Search pulse producingmeans for providing a, second potential in opposition to said biaspotential to render4 said electron tube means condutiveLand meansoperative thereafter to gradually.'reducesaid l second potential inmagnitudeata controlled rate.

5. In combination-in anecho distance measuring system having searchpulse producing means and echo pulse receivingmeans -operative at aprescribed frequency, an ,electronic ampliiier in circuit with saidreceivingmeans, said amplifier including a parallel-resonance `circuittuned substantially to vsaid prescribed frequency across.

which amplified received signals are developed, electron tube means'having ananode-cathode path connected in shuntwith saidparallelresonance circuit, means normally providing a cut-olf biaspotential to said electronv tube means, a source of second potential,switch means momentarily operated in synchronism with said search pulseproducing means for connecting said source to'said electron tube meansvin opposition to said bias potential to render said electron tube meansconductive.

6. In combination, in an echo distance measuring system having searchpulse producing means and echo pulse receiving means operative at aprescribed frequency, an electronic amplifier in circuit with saidreceiving means, said amplifier including a parallel-resonance circuittuned substantially to said prescribed frequency across which amplifiedreceived signals are developed, electron tube means having ananode-cathode path connected in shunt with said parallelresonancecircuit, means normally providing a cut-off bias potential to saidelectron tube means, a source of second potential, switch meansmomentarily operated in synchronism with said search pulse producingmeans for connecting said source to said electron tube means inopposition to said bias potential to render said electron tube meansconductive, charge storing means connected in parallel with said biasproaecomo viding means and arranged v to be. charged from said source'andi-'store-said Lsecond fpotential; and

means -for'discli'arging :saldi storing means ata controlled Crate.

7. In combinatiomin an echo` distance measuring systemhaving-search'pulse producing means and echo pulse. receiving' means.operative. at :a

prescribed frequency, ian .electronic amplier in circuit with'said;'receiving emeansvsaid amplifier including Ta parallel-resonance circuittuned substantially to said' prescribed frequency-across which famplified: received' signals are developed, electron tube means-havingananode, a cathode, and a control grid, 'with -its anode-cathode pathconnected in shunt with vsaid:parallel-resonance circuit,.a capacitoranda resistor connected in parallel between said cathode and saidcontrol grid, an'd means coupled in operation with said Search pulseproducing means for momentarily charging said 'capacitorin the directiontending to increase the conductivity of said electron tube means eachtime fa search pulse is produced, said resistor bein'g dimensioned todischarge said capacitor at'a controlled rate.

8. In'combination, in an echo 'distance measuring system havingsearchpulse producing means and Vecho pulse receiving means operative ata prescribed frequency-,S an 'electronic 'ampliiier in circuit withsaid' receiving'- means, said amplier including aparallel-res'onalnce'circuit tuned Sulzl stanti'ally to -s'id'prescribed frequency across which ampliiiedreceived fsignals aredeveloped,l

circuit means' connected infshunt with said parallei-resonance circuit,means' to produce a voltage pulse in synchronism with a search pulse,means employing said voltagevp'ulse to reduce th'e resistanc'e of said'shunthconnected means 'vvhen a search `Vpulse iSIprQdueed, and Vmeansoperative thereafter for gradually increasing said resistanceatacontr'olled'rate. l r A 9. vIn combination. in an echo distancemeasuring system having search pulse producing means and e'cho pulseVreceiving means operative at a prescribed frequency, an electronicamplifier in circuit with said receiving means, said amplier including aparallel-resonance circuit tuned substantially to said prescribedfrequency across which amplified received signals are developed,electron tube means having an anode-cathode path connected in shunt withsaid parallelresonance circuit, means to produce a voltage pulse insynchronism with a search pulse, means employing said voltage pulse toincrease the conductivity of said electron tube means when a searchpulse is' produced, and means operative thereafter -for graduallydecreasingsaid conductivity at a controlled rate.

10. In combination, in an echo distance measuring system having searchpulse producing means and echo pulse receiving means operative at-aprescribed frequency, an electronic amplier invcircuit with saidreceiving means. said amplifier including a parallel-resonance circuittuned substantially to said prescribedfrequency across which amplifiedreceived signals are developed, a rectifier connected in shunt with saidparallel-resonance circuit, means Acoupled with said search pulseproducing means for reducing the resistance' of said shunt-connected:rectier each time a search vpulse is produced, and means operativethereafter for gradually increasing said resistance at a controlledrate.

11. In combination, in an echo distance meas'- uring system havingsearch pulse producing means and echo vpulse receiving means operativeat a prescribed frequency, an electronic amplier in circuit with saidreceiving means, said amplier including a parallel-resonance circuittuned substantially to said prescribed `frequency across which ampliedreceived signals are developed, a rectifier connected in shunt with's'aid parallel-resonance circuit, means to produce a voltage pulse insynchronism with a' search pulse, means employing said voltage pulse,tol i'educethe resistance of said shunt-connected rec'tier when asearch pulse is produced, and means operative thereafter for graduallyincreasing "said resistance at a controlled rate.

' THOMAS J. BOLAND.

REFERENCES CITED The following references are' of record in the. le ofthis patent:

UNITED STATES PATENTS Posthumus May 9, 1950

